//双指针，关键在于如何优化

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
       vector<vector<int>> ret;
        sort(nums.begin(),nums.end());
        int n=nums.size();
        for(int i=0;i<n;)
        {
            if(nums[i]>0)break;
            int left=i+1,right=n-1;
            while(left<right)
            {
                int sum=nums[left]+nums[right]+nums[i];
                if(sum>0)
                {
                    right--;
                }
                else if(sum<0) left++;
                else{
                    ret.push_back({nums[i],nums[left],nums[right]});
                    left++;
                    right--;
                    while(left<right&&nums[left]==nums[left-1])left++;
                    while(left<right&&nums[right]==nums[right+1])right--;
                }
            }
             i++;
                while(i<n&&nums[i]==nums[i-1])i++;
        }
        return ret;
    }
};